Transcript for David Petraeus Resigns Over Affair With Biographer Paula Broadwell

new details on the affair that's brought down the head of the cia. The decorated and celebrated four-star general, david petraeus, once considered a possible presidential candidate. It started in an fbi investigation between e-mail between petraeus and his vid videograp videographer. We start with pierre thomas in washington. Reporter: The keeper of secrets was keeping a scandal of his own. And just like that, a storied military career and life of service to country. The resignation of the cia director stunned a city not easily shocked. One of the country's most respected and disciplined public officials left office admitting an indiscretion. In a statement to cia employees, petraeus acknowledged an affair. And what he called extremely poor judgment. Such behavior is unacceptable, the statement said. Both as a husband, and as a leader of an organization such as ours. On thursday, petraeus went to the white house to turn in his resignation. The same place he had so frequently been called on to serve. It is a great privilege to serve with our young men and women. Reporter: The affair was discovered by the fbi after concerns about inappropriate e-mails associated with petraeus surfaced. A focus of the probe turned to his biographer, paula broadwell. I think it was a good distraction from the war. Reporter: Petraeus had been the public face of two wars. One of the architects of the successful surge in iraq, which helped bring the war there to an end. From iraq to afghanistan. Then, the call to head the cia. Are you ready to come back? Ready for the cia? I feel very fortunate to have been provided such an opportunity to continue to serve and contribute, if confirmed. Reporter: As he took over cia, holly, his wife of 37 years, stood by his side, as she had done so many times before. The two had met at west point. She was from a long line of army royalty. Her great, great grandfather fought in the civil war. Her own father was a retired four-star general. The president phrased the direct director's dead dedication and patriotism. And his thoughts were with dave and holly petraeus. Now, it's the petraeus family that faces the strain of a deeply personal failure. But the nation's top spy has the to be above reproach. He had to go. Such a revelation was simply devastating. Bianna? Some people still stunned. Pierre, thank you. Now, to the woman at the center of the scandal. Biographer paula broadwell. It was the investigation into her that led to the downfall of petraeus. Broadwell had been public about what was described as an unusually close relationship with the general. Now, at some point, that relationship turned into an affair. Like petraeus, broadwell also had an impressive background. And now, a reputation in shambles. Our coverage continues with reena ninan. Reporter: They are both known as overachievers. As paula broadwell was making rounds in the media for her 400-page biographer about the four-star general. It's not the only one that the fbi is eager to learn more about their relationship. Paula broadwell, lifelong overachiever since high school in north dakota, where she was valedictorian and homecoming queen. Went on to receive honors for academic leadership at west point. And was ranked number one overall in fitness in her class. She spent some time in the black ops, got a free from harvard. And later, became biographer with david petraeus. Do you think he dropped his guard with you? Reporter: During a book tour this year, broadwell spoke about her access to petraeus, taping many of the interviews for her book, while running six-minute miles with the general. To get to know him, he wanted to run with you. I thought I would test him. But he was going to test me. But that was the foundation of our relationship. Reporter: That relationship, now placing the highly-accomplished 40-year-old mother of two in the center of a cia scandal. You seem to have a -- I don't know if special relationship is the right word. But he's taken a liking to you. Reporter: On wfae radio, she was fairful to protect her reputation, now tarnished. I think, you know, he was concerned a little bit about his legacy, as a leader naturally would be. And he was excited to have someone he could trust. Reporter: Married to radiologist, dr. Scott broadwell, she seemed as disciplined about her marriage as she is about her fitness. You can do it. Come on. Is this how arguments are settled in your house, by any chance? I don't win much. Reporter: Broadwell's 40th birthday was yesterday. She has 15 years of military service under her belt.

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